Magnetic recording device

ABSTRACT

A magnetic recording device includes: a magnetic recording medium containing a plurality of recording layers; a magnetic recording head for conducting magnetic writing of information in the magnetic recording medium; and a magnetic reproducing head for conducting magnetic reading out of the information from the magnetic recording medium; wherein the magnetic recording head includes a high frequency oscillator for magnetically assisting the magnetic writing of the information so as to change a magnetization of at least one of the plurality of recording layers of the magnetic recording medium, thereby recording a plurality of information different from one another in the magnetic recording medium commensurate with a total amount of magnetization of the plurality of recording layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2007-250166, filed on Sep. 26,2007; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording device realizingmulti-data recording.

2. Description of the Related Art

The development in high density recording and large capacity of amagnetic recording drive (Hard disk drive) influences the growth of aportable music media player and a video recorder in addition to a PC anda server. The degree of distribution of the magnetic recording devicedepends on the capacity of the magnetic recording device. The key pointenhancing the capacity of the magnetic recording device almost dependson the enhancement of the recording density.

As an index relating to the recording density, a unit of bit number persquare inch, that is, bit/inch² (bpsi) is employed. As of now, therecording density is being enhanced by reducing the size per bit. Withthe bit size reduction, if the recording density reaches several Tbpsi,the line size per bit becomes 10 nm or less.

However, it is obvious the reduction in line size per bit by theconventional technique has its limitation as follows.

In order to read out small bits, the element size of a magnetic head tobe employed is required to be downsized. Then, the element size of themagnetic head depends on the minimum line width limitation inphotolithography technique. If the photolithography technique isdeveloped so as to reduce the bit size, it becomes difficult the bitdata stored in the corresponding bits formed in a magnetic recordingmedium are maintained originated from the heat fluctuation of themagnetic recording medium. Moreover, if a material with a highermagnetic anisotropy can be developed, bits formed at a magneticrecording medium made of the material can not be inverted by a magnetichead so that the intended magnetic recording can not be realized. Inaddition, if the bit size is set to 10 nm or less, the inherent magneticfeature of the material forming the magnetic recording medium can not beexhibited because the total number of atoms in the material contributingto the bit formation is decreased. In other words, if the material withthe higher magnetic anisotropy is developed, the inherent magneticfeature of the material can be exhibited within a bit size range of 20to 30 nm, but not within a bit size range of 10 nm or less.

According to the conventional technique of reducing the size per bit,the high density recording not only in the magnetic recording device butalso in a storage device has its limitation in itself.

As described above, it is obvious the high density recording techniquehas its physical limitation by means of the reduction in bit size. Inorder to realize the high density recording not utilizing the reductionin bit size, multi-data recording and multi-layer recording can beexemplified as semiconductor memory technical field. In this case, sincemultiple data can be stored per area corresponding to 1 bit/1 pattern inthe magnetic recording medium, the recording density can be enhanced.

It is difficult, however, to apply the multi-data recording techniqueand the multi-layer recording technique to the magnetic recordingtechnical field, different from the semiconductor memory technicalfield.

With the multilayer recording technique, a semiconductor memory isconfigured such that a plurality semiconductor chips are stacked so asto be electrically connected with one another with electric wires. Inthis case, the multilayer recording can be realized by flowing a currentselectively in one or more of the electric wires. In this case, it isrequired to form the multiple wires for realizing the electricalconnection by means of minute processing technique. Since the minuteprocessing technique is complicated, it is difficult to form themultiple wires, but the intended multi-layer recording can be realizedin principle by the multiple wires.

In the magnetic recording device, however, no magnetic wire can beformed between the magnetic head and the magnetic recording medium. Inthis case, since it is required to dispose the magnetic head away fromthe magnetic recording medium, a minute space is formed between themagnetic head and the magnetic recording medium. In this point of view,the selective bit formation can not be realized using the magnetic wireso that some bits may be formed in the area of the magnetic recordingmedium in the vicinity of the magnetic head when intended bits areformed in the area away from the magnetic recording medium. Namely,suppose that the magnetic recording medium contains a plurality ofrecording layers, when the magnetic recording is carried out for thelower recording layer, the magnetic recording is also carried out forthe upper recording layer so that some bits may be formed at the upperrecording layer in addition to the lower recording layer. Therefore, theselective magnetic recording for the upper recording layer and the lowerrecording layer can not be realized. In the magnetic recording device,as a result, it is difficult to realize the multi-layer recording inprinciple.

With the multi-data recording technique, the bit information stored inthe corresponding bit is recognized as a numeral “1” or “0” commensuratewith the direction in magnetization of the bit. In order to realize themulti-data recording, in this point of view, it is required to set thedirection in magnetization of the bit to zero degree meaning that thebit magnetization is oriented parallel to the surface of the magneticrecording medium, 45 degrees meaning that the bit magnetization isoriented in inclination from the direction perpendicular to the surfaceof the magnetic recording medium and the like. However, it is verydifficult to realize the state where the bit magnetization is orientedparallel to the surface of the magnetic recording medium, the statewhere the bit magnetization is oriented in inclination from thedirection perpendicular to the surface of the magnetic recording mediumand the like. As of now, there is no technique to realize theabove-described bit magnetization states. As a result, it is verydifficult to realize the multi-data recording in the magnetic recordingdevice.

BRIEF SUMMARY OF THE INVENTION

An aspect of the present invention relates to a magnetic recordingdevice, including: a magnetic recording medium containing a plurality ofrecording layers; a magnetic recording head for conducting magneticwriting of information in the magnetic recording medium; and a magneticreproducing head for conducting magnetic reading out of the informationfrom the magnetic recording medium; wherein the magnetic recording headincludes a high frequency oscillator for magnetically assisting themagnetic writing of the information so as to change a magnetization ofat least one of the plurality of recording layers of the magneticrecording medium, thereby recording a plurality of information differentfrom one another in the magnetic recording medium commensurate with atotal amount of magnetization of the plurality of recording layers.

Another aspect of the present invention relates to a magnetic recordingdevice, including: a magnetic recording medium containing a plurality ofrecording layers; a magnetic recording head for conducting magneticwriting of information in the magnetic recording medium; and a magneticreproducing head for conducting magnetic reading out of the informationfrom the magnetic recording medium; wherein the magnetic reproducinghead is configured so as to detect an intensity of a magnetic fieldcaused from a total amount of magnetization of the plurality ofrecording layers of the magnetic recording medium and then, read out aplurality of information different from one another which are recordedin the magnetic recording medium.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an explanatory view showing the magnetic recording statesrelating to numeral “0” and “1” bit information in a magnetic recordingmedium of a conventional magnetic recording device.

FIG. 2 is an explanatory view showing the magnetic recording states in amagnetic recording medium of a magnetic recording device according to anembodiment.

FIGS. 3A-3C are explanatory views showing the magnetic recording statesin corresponding recording layers in the magnetic recording medium ofthe magnetic recording device according to the embodiment.

FIG. 4 is a structural view schematically showing a magnetic recordingmedium of a magnetic recording device according to an embodiment.

FIG. 5 is a structural view schematically showing a magnetic recordingmedium of a magnetic recording device according to another embodiment.

FIG. 6 is a structural view schematically showing a magnetic recordingmedium of a magnetic recording device according to still anotherembodiment.

FIG. 7 is a structural view schematically showing a magnetic recordingmedium of a magnetic recording device according to a further embodiment.

FIG. 8 is a schematic view for explaining a recording method using amagnetic head in a magnetic recording device according to an embodiment.

FIG. 9 is a structural view schematically showing the structure of amagnetic head to be employed in a magnetic recording device according toan embodiment.

FIG. 10 is a structural view schematically showing the structure ofanother magnetic head to be employed in a magnetic recording deviceaccording to an embodiment.

FIG. 11 is a structural view schematically showing the structure ofstill another magnetic head to be employed in a magnetic recordingdevice according to an embodiment.

FIG. 12 is a structural view schematically showing the structure of afurther magnetic head to be employed in a magnetic recording deviceaccording to an embodiment.

FIG. 13 is a structural view schematically showing the structure of ahigh-frequency oscillator to be employed in a magnetic recording deviceaccording to an embodiment.

FIG. 14 is a structural view schematically showing the structure ofanother high-frequency oscillator to be employed in a magnetic recordingdevice according to an embodiment.

FIG. 15 is a structural view schematically showing the structure ofstill another high-frequency oscillator to be employed in a magneticrecording device according to an embodiment.

FIG. 16 is a structural view schematically showing the structure of afurther high-frequency oscillator to be employed in a magnetic recordingdevice according to an embodiment.

FIG. 17 is a structural view schematically showing the structure of astill further high-frequency oscillator to be employed in a magneticrecording device according to an embodiment.

FIG. 18 is a structural view schematically showing the structure ofanother high-frequency oscillator to be employed in a magnetic recordingdevice according to an embodiment.

FIG. 19 is a schematic view showing the structure of a magneticrecording/reproducing device including a magnetic head to be employedaccording to an embodiment.

FIG. 20 is a schematic view showing a magnetic head assembly to be builtin the magnetic recording/reproducing device shown in FIG. 19.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail withreference to the drawings.

(Principles of Multi-Layer Recording and Multi-Data Recording)

First of all, the principles of multi-layer recording and multi-datarecording in a magnetic recording device according to an embodiment willbe described referring to a conventional magnetic recording device.

(Reproducing)

FIG. 1 is an explanatory view showing the magnetic recording statesrelating to numeral “0” and “1” bit information in a magnetic recordingmedium of a conventional magnetic recording device. As shown in FIG. 1,the numeral “0” or “1” bit information is recorded in a magneticrecording medium of the magnetic recording device commensurate with thedirection in magnetization of bit. In this case, the numeral “1” isallotted to the magnetization state of bit directed upward in thedirection perpendicular to the surface of the magnetic recording mediumand the numeral “0” is allotted to the magnetization state of bitdirected downward in the direction perpendicular to the surface of themagnetic recording medium. Alternatively, the numeral “0” is allotted tothe magnetization state of bit directed upward in the directionperpendicular to the surface of the magnetic recording medium and thenumeral “1” is allotted to the magnetization state of bit directeddownward in the direction perpendicular to the surface of the magneticrecording medium.

The above-mentioned bit recording can be performed for a Discrete Trackmedium (DTM) where adjacent tracks are separated with non-magneticmaterial and a Bit Patterned medium (BPM) where adjacent tracks andadjacent bits are separated with non-magnetic material, respectively, aswell as a continuous magnetic medium as a standard medium commerciallyavailable.

As a magnetic head to detect the bit information, a magneto-resistanceeffect element is employed at present. The resistance of themagneto-resistance effect element is changed in accordance with anexternal magnetic field when a current is flowed in themagneto-resistance effect element. As the magneto-resistance effectelement, as of now, a CIP-GMR (current-in-plane giant magnetoresistive)film is widely employed, and recently, a TMR (tunnelingmagnetoresistive) film is also employed. In the future, a CPP-GMR(current-perpendicular-to-plane) film will be promised as themagneto-resistance effect element. In the exemplified elements, the bitinformation can be detected by the changes in resistance of the elementswhen currents are flowed in the elements as described above. The numeral“0” and “1” bit information can be detected by recognizing the higherresistance state and the lower resistance state of themagneto-resistance effect element.

FIG. 2 is an explanatory view showing the magnetic recording states in amagnetic recording medium of a magnetic recording device according to anembodiment. In order to realize the multi-data recording for themagnetic recording medium, as shown in FIG. 2, a larger upwardmagnetization state and a smaller upward magnetization state are formed(refer to left side in FIG. 2), and a larger downward magnetizationstate and a smaller downward magnetization state are formed (refer toright side in FIG. 2). Then, the formation of the larger magnetizationstate and the smaller magnetization state will be described in detailhereinafter.

The larger magnetization state and the smaller magnetization state inthe magnetic recording medium correspond to an external larger magneticfield and an external smaller magnetic field in the magneto-resistanceeffect element. Herein, the larger magnetization state and the smallermagnetization state are originated from the remanent verticalmagnetization of the magnetic recording medium. In this case, since itcan be considered that there are a plurality of external magnetic fieldswith respective different intensities to be applied to themagneto-resistance effect element, the resistance of themagneto-resistance effect element is changed in accordance with thedifferent intensities of the magnetic fields so that in FIG. 2, four bitinformation of numeral “0”, “1”, “2” and “3” can be recognized.

The recognition of four bit information using the change in resistanceof the magneto-resistance effect element can not be realized when thechange in resistance of the magneto-resistance effect element, that is,the MR ratio, is relatively small, but can be realized when the MR ratiois relatively large. For example, when the magneto-resistance effectelement is made using the principle of the CIP-GMR film, the TMR film orthe CPP-GMR film, the recognition of four bit information can berealized. Any film can be employed as the magneto-resistance effectelement only if the MR ratio of the film caused by the external magneticfield is large. Furthermore, a new magneto-resistance effect elementexhibiting MR effect based on a quite different principle from theprinciples of the CIP-GMR film, the TMR film and the CPP-GMR film may beemployed. Anyway, any film using any principle may be employed as themagneto-resistance effect element.

The larger magnetization state and the smaller magnetization stateoriginated from the remanent vertical magnetization can not be realizedin a conventional magnetic recording medium. In this point of view, itis required the conventional magnetic recording medium is devised todevelop a new magnetic recording medium. The fundamental principle ofthe new magnetic recording medium will be described in reference to FIG.3.

FIG. 3A shows the magnetization state per bit relating to the remanentmagnetization per bit. FIG. 3B shows the concrete structure forrealizing the magnetization state per bit shown in FIG. 3A. It isnecessarily required that a plurality of magnetic recording layers areprovided and the adjacent magnetic recording layers are separated withrespective magnetic separating layers for realizing the magnetizationstate shown in FIG. 3B. Each magnetic recording film is made of a hardmagnetic film. Since the adjacent magnetic recording layers areseparated with the corresponding magnetic separating layers, themagnetic recording layers are magnetically separated from one another sothat recording operation can be conducted independently per magneticrecording layer. Bits relating to information to be recorded are formedin one or more of the magnetic recording layers. The magnetic separatinglayer may be made of a material containing non-magnetic element. As thenon-magnetic element, Ru, Pd, Ir and Pt may be exemplified.

In the case that two magnetic recording layers are provided as shown inFIG. 3B, an upward magnetization and a downward magnetization can beformed in the upper magnetic recording layer and the lower magneticrecording layer, respectively. In view of the combination of the uppermagnetic recording layer and the lower magnetic recording layer, fourmagnetization states can be formed. In this case, if the magneticthickness of the upper magnetic recording layer is set equal to themagnetic thickness of the lower magnetic recording layer, the upwardmagnetization in the upper magnetic recording layer is cancelled by thedownward magnetization in the lower magnetic recording layer while thedownward magnetization in the upper magnetic recording layer iscancelled by the upward magnetization in the lower magnetic recordinglayer. As viewed from the outside of the magnetic recording layers,therefore, no magnetic field is leaked therefrom. As a result, theupward magnetization and the downward magnetization in the uppermagnetic recording layer and the lower magnetic recording layer can notbe apparently recognized. Herein, the “magnetic thickness” can berepresented by “Mrδ” (Mr: remanent magnetization, δ: thickness ofmagnetic recording layer).

In order to recognize the combination of the upward magnetization andthe downward magnetization in the upper magnetic recording layer and thelower magnetic recording layer, in this point of view, it is requiredthat the magnetic thickness Mrδ of the upper magnetic recording layer isset different from the magnetic thickness Mrδ of the lower magneticrecording layer. The magnetic thickness of the upper magnetic recordinglayer may be set larger than the magnetic thickness of the lowermagnetic recording layer, or vice versa. In FIG. 3B, the thickness ofthe upper magnetic recording layer is set larger than the thickness ofthe lower magnetic recording layer so that the magnetic thickness Mrδ ofthe upper magnetic recording layer can be set larger than the magneticthickness Mrδ of the lower magnetic recording layer. In this case, fourbit information recording relating to four remanent magnetic states inthe combination of the upper magnetic recording layer and the lowermagnetic recording layer can be realized.

According to the above-described fundamental principle about themulti-data recording, if the number of magnetic recording layers is setto three or more, eight bit information recording can be realized. FIG.3C shows the state where three magnetic recording layers are provided.The adjacent magnetic recording layers are magnetically separated withrespective magnetic separating layers. Then, the magnetic thicknesses ofthe magnetic recording layers are set different from one another so asto realize the eight bit information recording as shown in FIG. 3C. Thereproducing operation of the eight bit information recording can beconducted using a magneto-resistance effect element in the same manneras the embodiments relating to FIG. 2. In this case, since eightresistances can be obtained from the eight bit information, the magnetichead (magneto-resistance effect element) can detect each of the eightbit information by recognizing the eight resistances.

In this embodiment, the magnetic recording medium containing themagnetic recording layers can be configured as a continuous medium wherethe films constituting the magnetic recording layers are uniformlyformed two-dimensionally over the surface of the disk, a Discrete Trackmedium where the adjacent tracks are magnetically separated withrespective non-magnetic materials, or a Bit patterned medium where theadjacent tracks and the adjacent bits are magnetically separated withrespective non-magnetic materials. FIG. 4 shows the structure of thecontinuous medium according to an embodiment. FIG. 5 shows the structureof the Discrete medium according to an embodiment. FIG. 6 shows thestructure of the Bit Patterned medium according to an embodiment.

With the continuous medium, the magnetic recording layers are formedover the surface of the disk so that the area to be recorded (bitformation area) is made of the same magnetic material of the area to benot recorded (bit unformation area). The bit formation area is definedby conducting the writing operation with the recording head and the bitunformation area is defined by not conducting the writing operation withthe recording head. In FIG. 4, the bit unformation area is not clearlydepicted, but formed between the adjacent tracks and the adjacent bits.As described above, the bit unformation area is made of the samematerial as the bit formation area. With the Discrete Track medium, theadjacent tracks are magnetically separated with respective non-magneticmaterials (not shown). With the Bit Patterned medium, the adjacenttracks and the adjacent bits are magnetically separated with respectivenon-magnetic materials. In view of the reproducing principle, any typeof magnetic medium will do. In view of the recording principle, one ormore of the magnetic recording media may exhibit some advantages incomparison with the other(s) of the magnetic recording media, which willbe described later.

In FIGS. 4 to 6, although only the magnetic separating layers formagnetically separating the magnetic recording layers are depictedexcept the magnetic recording layers, naturally, a protective layerand/or a lubricant layer may be formed on the top magnetic recordinglayer and a backing magnetic layer for realizing the vertical magneticrecording may be formed on the bottom magnetic recording layer via anon-magnetic underlayer. FIG. 7 shows the stacking structure below thetop magnetic recording layer of a magnetic recording medium according toan embodiment.

In FIG. 7, the magnetic recording layers 1 to 3 are stacked via themagnetic separating layers 4 and 5. Then, the underlayer 6 forcontrolling the crystallinities of the magnetic recording layers 1 to 3is formed on the bottom surface of the magnetic recording layer 3. Theunderlayer 6 can be called as an underlayer for the magnetic recordinglayers. It is desired that the underlayer 6 is made of non-magneticmaterial so as to magnetically separate the magnetic recording layer 3and the backing magnetic layer 7 to be formed on the bottom surface ofthe underlayer 6. Then, the backing magnetic layer 7 is formed on thebottom surface of the underlayer 6. With the vertical magneticrecording, when the magnetic recording head is considered as a magneticpole, the backing magnetic layer 7 can be considered as another magneticpole. In this point of view, the backing magnetic layer 7 is made ofsoft magnetic material. Then, the backing layer 7 is formed on theunderlayer 8 for controlling the crystallinity of the backing magneticlayer 7. The underlayer 8 can be called as an underlayer for the backingmagnetic layer 7. Then, the medium substrate made of glass substrate oraluminum substrate (not shown) is provided on the bottom surface of theunderlayer 8.

<Recording>

Then, the recording method using a recording head for realizing themulti-data recording will be described. The multi-data recording can notbe realized by a conventional recording head. When the magnetic fieldfor recording is applied to the magnetic medium from the conventionalrecording head, all of the magnetic recording layers are magnetized inthe same direction because the magnetic field is oriented in the samedirection. In the embodiment relating to FIG. 3B, concretely, when it isintended recording operation is conducted for the lower magneticrecording layer by applying a magnetic field to the lower magneticrecording layer, the upper magnetic recording layer is also magnetizedin addition to the lower magnetic recording layer because the magneticfield is also applied to the upper magnetic recording layer in additionto the lower magnetic layer. Therefore, the two-layered structurebecomes meaningless in view of the multi-data recording, and thus, theintended multi-data recording can not be realized.

In this point of view, the structure of a recording head for realizingthe multi-data recording will be illustrated in FIG. 8. The magneticrecording head in FIG. 8 conducts a high frequency assist recordingusing a high frequency oscillator configured such that the oscillatingfrequency is variable in addition to a recording magnetic pole.According to the magnetic recording head shown in FIG. 8, the selectiverecording can be conducted for the magnetic recording layersirrespective of the positions of the magnetic recording layers. Theprinciple of the high frequency assist recording will be described.

First of all, the principle of a conventional high frequency assistrecording will be described. Referring to Reference 1, a direct currentis flowed perpendicular to the film surface of the stacking structure atleast made of a magnetic layer/a non-magnetic layer/a magnetic layer tocause a high frequency oscillation based on the spin torque effect, andthen, the intensity of a magnetic field for recording is reduced usingthe high frequency oscillation as an energy assist source. If thefrequency of the high frequency oscillation is set almost equal to themagnetic resonance frequency of the magnetic recording medium, theassist effect of the high frequency oscillation is enhanced to reducethe intensity of the magnetic field for recording (inverting themagnetization of a magnetic recording layer).

-   [Reference 1] Jian-Gang Zhu et al, CMU, B6, “Microwave Assisted    Magnetic Recording for 1 Terabit/in² Density and Beyond”, The    18^(th) International Conference on Magnetic Recording Heads and    Systems, May 21-23, 2007, Minneapolis, Minn., USA.

The inventors found out that the multi-data recording can be realizedwhen the high frequency assist recording is devised to some degrees.First of all, the magnetic resonance frequencies of the magneticrecording layers are set different from one another as a preconditionfor realizing the multi-data recording. In this case, when a highfrequency oscillation is conducted from the high frequency oscillator,the high frequency oscillation affects one of the magnetic recordinglayers as an energy assist and dose not affect the others of themagnetic recording layers as an energy assist.

As shown in FIG. 8, in this embodiment, the high frequency oscillator isdisposed in the vicinity of the magnetic recording pole. A highfrequency assist magnetic field with a predetermined high frequency isgenerated from the high frequency oscillator at the same time when arecording magnetic field is generated from the magnetic recording pole.Concretely, when a high frequency assist magnetic field almost equal tothe ferromagnetic resonance frequency of one of the magnetic recordinglayers is oscillated from the high frequency oscillator, the intendedmagnetic recording layer can be assisted in energy so as to bemagnetically recorded even though the recording magnetic field is setsmaller than a recording magnetic field required for magnetic recording.

Herein, if all of the magnetic recording layers are made of the samematerial, all of the magnetic recording layers are assisted in energy bythe same high frequency assist magnetic field so that only the intendedmagnetic recording layer can not be recorded. In the embodiment shown inFIG. 8, when the high frequency assist magnetic field with the highfrequency f2 almost equal to the ferromagnetic resonance frequency f2′of the magnetic recording layer 2 is applied to the magnetic recordinglayer 2, only the magnetic recording layer 2 is assisted in energy so asto be recorded (the magnetization is inverted) by the recording magneticfield H. Since the intensity of recording magnetic field H is setsmaller than the intensities of recording magnetic fields requiring forrecording the magnetic recording layers 1 and 3, the magnetic recordinglayers 1 and 3 can not be recorded by the recording magnetic field Hunder no ferromagnetic resonance frequency.

The recording operation for the magnetic recording layers 1 and 3 can beconducted in the same manner as the magnetic recording layer 2. In thecase that the recording operation is conducted for the magneticrecording layer 1, the high frequency assist magnetic field with thehigh frequency f1 almost equal to the ferromagnetic resonance frequencyf1′ of the magnetic recording layer 1 is generated from the highfrequency oscillator and then, the recording magnetic field H is alsogenerated from the magnetic recording pole. In the case that therecording operation is conducted for the magnetic recording layer 3, thehigh frequency magnetic field with the high frequency f3 almost equal tothe ferromagnetic resonance frequency f3′ of the magnetic recordinglayer 3 is generated from the high frequency oscillator and then, therecording magnetic field H is also generated from the magnetic recordingpole.

It is amenable design concept that the frequencies f1 to f3 of the highfrequency magnetic fields are set almost equal to the ferromagneticresonance frequencies f1′ to f3′ of the magnetic recording layers 1 to 3because the high frequency assist magnetic field can be utilizedeffectively and efficiently for the magnetic recording for the intendedmagnetic recording layer. Herein, if the high frequency assist magneticfields f1 to f3 are set within the ranges of the ferromagnetic resonancefrequencies f1′ to f3′±1 GHz or less, the above-described magneticrecording utilizing the ferromagnetic resonances of the magneticrecording layers can be conducted.

Alternatively, the magnetic recording utilizing the high frequencyenergy assist can be realized if the high frequencies f1 to f3 in thehigh frequency assist magnetic field are not set almost equal to theferromagnetic resonance frequencies f1′ to f3′. Concretely, when a highfrequency assist magnetic field with a high frequency of integralmultiplication of (½)×ferromagnetic resonance frequency (e.g.,ferromagnetic resonance frequency f1′) as represented byn×(½)×ferromagnetic resonance frequency is applied to the intendedmagnetic recording layer, the intended magnetic recording layer can berecorded under high frequency energy assist. In view of the use of thehigh frequency assist magnetic field with the high frequencies f2 andf3, the magnetic recording can be conducted in the same manner asdescribed above.

In order to change the ferromagnetic resonance frequency, it is mosteffective to change the material constituting the magnetic recordinglayer. As well known, the ferromagnetic resonance frequency of themagnetic material is increased as the magnetic anisotropy of themagnetic material is increased.

In this point of view, it is turned out that the ferromagnetic resonancefrequency of the ferromagnetic material is changed commensurate with themagnetic anisotropy of the ferromagnetic material. The magneticanisotropy of the ferromagnetic material can be controlled by adjustingthe sort and amount of additive element in the ferromagnetic materialand forming another ferromagnetic material layer on the ferromagneticmaterial.

It is desired that the ferromagnetic resonance frequencies of themagnetic recording layers are different from one another by at least 1GHz or more. In this case, the magnetic recording utilizing the highfrequency energy assist as described above can be easily realized sothat the magnetic recording layers can be selectively recorded with thehigh frequency assist magnetic field and the recording magnetic field.

In order to satisfy the above-described requirement of the ferromagneticresonance frequencies of the magnetic recording layers being differentfrom one another by at least 1 GHz or more, it is desired that themagnetic recording layers contain at least one element selected from thegroup consisting of Co, Fe, Ni and Fe such that the contents in theselected element of the magnetic recording layers are different from oneanother by five atomic % or more.

As apparent from the recording principle as described above, it isnecessarily required for the high frequency oscillator that theoscillating frequency of the high frequency oscillator can be changedappropriately, which is important function for the high frequencyoscillator. The variable range of the oscillating frequency is set suchthat when a high frequency assist magnetic field with a predeterminedhigh frequency is applied to a magnetic recording layer, ferromagneticresonance is caused in the magnetic recording layer and no ferromagneticresonance is caused in other magnetic recording layers. Concretely, thevariable range of the oscillating frequency is set to the order of 1 GHzor more. An embodiment relating to the high frequency oscillatorsatisfying the above-described requirement will be described.

<Magnetic Recording Medium>

Any magnetic recording medium can be used only if the magnetic recordingmedium contains a plurality of magnetic recording layers so as torealize the multi-layer recording and multi-data recording through thedifferent magnetic intensities of the magnetic recording layers relatingto the data information. For example, a continuous film medium with arecording layer formed over the surface of a disk may be employed as themagnetic recording medium. Alternatively, a Discrete Track medium ofwhich the adjacent tracks are separated with corresponding non-magneticmaterials and a Bit Patterned medium of which the adjacent tracks andthe adjacent bits are separated with corresponding non-magneticmaterials may be employed as the magnetic recording medium.

With the Discrete Track medium and the Bit Patterned medium, since theareas to be recorded is separated with the non-magnetic materials, theferromagnetic resonance may be caused and concentrated only in the areasto be recorded when the high frequency assist magnetic field is applied.With the Discrete Track medium and the Bit Patterned medium, the areasto be recorded are made of metallic material and other areas not to berecorded such as the areas between the tracks and the areas between thebits are made of insulating material, the high frequency assist magneticfield can be effectively applied to the areas to be recorded so as to beeffectively applied to the recording bit areas. The continuous filmmedium, the Discrete Track medium and the Bit Patterned medium may beconfigured as shown in FIGS. 4 to 6.

<Overall Structure of Magnetic Head>

Then, the overall structure of a magnetic head to be employed in themagnetic recording device in this embodiment will be described. FIGS. 9to 12 show the magnetic head schematically.

In FIG. 9, the magnetic head includes a reproducing section 10containing a magneto-resistance effect element 11, a top shield 12 and abottom shield 13 sandwiching the magneto-resistance effect element 11,and a recording section 20 containing a recording magnetic pole 21, ayoke 22 with which the rear end of the recording magnetic pole 21 isconnected, a coil 23 wound around the recording magnetic field 21 so asto generate a recording magnetic field and a high frequency oscillator25 disposed between the recording magnetic field 21 and the yoke 22. Thereproducing section 10 is disposed in the vicinity of the recordingsection 20.

The magnetic head shown in FIG. 10 is configured similar to the magnetichead shown in FIG. 9 except that the high frequency oscillator 25 isdisposed outside the recording magnetic pole 21 in the recording section20. The magnetic head shown in FIG. 11 is configured similar to themagnetic head shown in FIG. 10 except that the top shield 12 in thereproducing section 10 also functions as the yoke 22 in the recordingsection 20. The magnetic head shown in FIG. 12 is configured similar tothe magnetic head shown in FIG. 11 except that the magneto-resistanceeffect element 11 in the reproducing section 10 also functions as thehigh frequency oscillator 25 in the recording section 20.

As described hereinafter, since the film structure of themagneto-resistance effect element is similar to the film structure ofthe high frequency oscillator, the magneto-resistance effect element 11can also function as the high frequency oscillator 25 as shown in FIG.12. In this case, the period of time requiring for forming the magnetichead can be reduced remarkably so that the yield ratio of the magnetichead can be enhanced. At reproducing, a driving current is flowed in themagneto-resistance effect element 11 so as to exhibit the inherentreproducing function. At recording, another driving current is flowed inthe magneto-resistance effect element 11 so as to exhibit the highfrequency oscillating function so that the magneto-resistance effectelement 11 can function as the high frequency oscillator constituting ahigh frequency assist source. The driving current at reproducing isdifferent from the driving current at recording. Concretely, the drivingcurrent at recording is set higher than the driving current atreproducing.

Any type of magnetic head can be employed only if the multi-layerrecording and the multi-data recording can be realized.

<High Frequency Oscillator>

Then, a high frequency oscillator to be employed in the magneticrecording device in this embodiment will be concretely described. FIG.13 is a structural view schematically showing the high frequencyoscillator.

In FIG. 13, the high frequency oscillator 25 is configured such that anunderlayer 252, a pinning layer 253, a first pinned layer 254, amagnetic coupling layer 255, a second pinned layer 256, a spacer layer257, a free layer 258 and a cap layer 259 are subsequently stacked froma bottom electrode 251 to a top electrode 260. The pinning layer 253through the free layer 258 constitute a CCP (Current Perpendicular toPlane) type spin valve structure. The top electrode 260 and the bottomelectrode 251 constitute a pair of electrodes for flowing a current inthe spin valve structure along the stacking direction (that is,vertically).

The magnetization of the first pinned layer 254 is magnetically fixedwith the magnetization of the pinning layer 253 and the second pinnedlayer 256 is antiferromagnetically coupled with the first pinned layer254 via the magnetic coupling layer 255 so that the spin valve structureconstitutes a synthetic antiferromagnetic (or syntheticantiferrimagnetic) structure.

In the high frequency oscillator 25, the three-layered structure made ofthe second pinned layer 256, the spacer layer 257 and the free layer 258causes a high frequency oscillation originated from the spin torqueeffect as described above. The high frequency oscillation functions asenergy assist so as to reduce the intensity of a recording magneticfield for a recording medium.

The bottom electrode 251 and the top electrode 260 are made of lowelectric resistance material such as NiFe and Cu.

The underlayer 252 can be divided into a buffer layer and a seed layer.The buffer layer functions as reducing the surface roughness of bottomelectrode 251. The seed layer functions as controlling the crystalorientation and crystal grain size of the spin valve film to be formedthereon. The buffer layer may be formed of Ta, Ti, W, Zr, Hf, Cr or analloy thereof in a thickness of 2 to 10 nm, preferably 3 to 5 nm. Theseed layer may be formed of Ru or NiFe which can exhibit fcc structure(face-centered cubit structure), hcp structure (hexagonal close-packedstructure) or bcc structure (body-centered cubic structure) in athickness of 1 to 5 nm, preferably 3 to 5 nm.

The pinning layer 253 imparts unidirectional anisotropy to the firstpinned layer 254 to be formed thereon so that the magnetization of thefirst pinned layer 254 is magnetically fixed with the unidirectionalanisotropy. For example, the pinning layer 253 is formed ofantiferromagnetic material such as PtMn, PdPtMn, IrMn and RuRhMn in athickness of several nm to several ten nm. The appropriate thickness ofthe pinning layer 253 depends on the sort of the constituent materialthereof.

The first pinned layer 254 and the second pinned layer 256 may be madeof ferromagnetic material such as CoFe and NiFe. The magnetic couplinglayer 255 may be made of non-ferromagnetic material such as Ru and Cu.The three-layered structure of the first pinned layer 254, the magneticcoupling layer 255 and the second pinned layer 256 may be made of, e.g.,Co₉₀Fe₁₀ 3.5 nm/Ru/(Fe₅₀Co₅₀ 1 nm/Cu 0.25 nm)×2/Fe₅₀Co₅₀ 1 nm.

The spacer layer 257 is made of oxide, nitride or oxynitride. Forexample, the spacer layer 257 may be made of amorphous Al₂O₃ or crystalMgO. In view of the inherent function of the spacer layer, the thicknessof the spacer layer 257 is set within a range of 1 to 3.5 nm, preferably1.5 to 3 nm. Moreover, an additive element such as Ti, Hf, Mg, Zr, V,Mo, Si, Cr, Nb, Ta, W, B, C and V may be added to the spacer layer 257.The content of the additive element may be set within a range of 0 to50%. In an embodiment, the spacer layer 257 may be made of Al₂O₃ layerwith a thickness of about 2 nm.

The spacer layer 257 may be made of Ti oxide, Hf oxide, Mg oxide, Zroxide, Cr oxide, Ta oxide, Nb oxide, Mo oxide, Si oxide or V oxideinstead of Al oxide such as Al₂O₃. In these cases, the additive elementmay be added to the spacer layer 257 within a content range of 0 to 50%.

The free layer 258 is configured so as to cause the spin torque effect,and thus, made of a two-layered structure of Co₉₀Fe₁₀ 1 nm/Ni₈₃Fe₁₇ 3.5nm. The layered structure is formed by disposing the CoFe layer at theinterface between the NiFe layer and the spacer layer 257. Moreover, itis desired that the CoFe layer is formed in the vicinity of the spacerlayer 257 in comparison that the NiFe layer is formed in the vicinity ofthe spacer layer 257. The free layer 258 may be made of a multilayeredstructure formed by alternately stacking CoFe layers or Fe layers eachthickness being set within a range of 1 to 2 nm and thinnest Cu layerseach thickness being set within a range of 0.1 to 0.8 nm, respectively.

The cap layer 259 functions as protecting the spin valve structure. Thecap layer 259 may be made of a plurality of metallic layers, e.g., atwo-layered structure of Cu 1 nm/Ru 10 nm. Alternatively, the cap layer259 may be made of another two-layered structure of Ru 0.5 to 2 nm/Cu bydisposing the Ru layer in the vicinity of the free layer 258. The caplayer 259 of the two-layered structure of Ru/Cu is desired when the freelayer 258 is made of NiFe because elemental Ru is not solid-solved into(mixed with) elemental Ni so that the magnetostriction originated fromthe interface mixing layer formed between the free layer 258 and the caplayer 259 can be reduced.

FIG. 14 is a structural view schematically showing another highfrequency oscillator to be employed in the magnetic recording device inthis embodiment. The high frequency oscillator 25 shown in FIG. 14 isconfigured similar to the high frequency oscillator 25 except that thespacer layer 257 contains an insulating layer 257A, current paths 257B,a bottom metallic layer 257C and a top metallic layer 257D. In thisembodiment, therefore, the spacer layer 258 will be described in detailso that the explanations for other components will be omitted.

The insulating layer 257A is made of oxide, nitride or oxynitride. Forexample, the spacer layer 257 may be made of Al₂O₃-based material, asoccasion demands, containing an additive element such as Ti, Hf, Mg, Zr,V, Mo, Si, Cr, Nb, Ta, W, B, C and V. The content of the additiveelement may be set within a range of 0 to 50%. In an embodiment, theinsulating layer 257A may be made of Al₂O₃ layer with a thickness ofabout 2 nm. The insulating layer 257A may be made of Ti oxide, Hf oxide,Mg oxide, Zr oxide, Cr oxide, Ta oxide, Nb oxide, Mo oxide, Si oxide orV oxide instead of Al oxide such as Al₂O₃. In these cases, the additiveelement may be added to the spacer layer 257 within a content range of 0to 50%.

The current paths 257B are paths for flowing a current perpendicular tothe film surface of the spacer layer 257. In this case, the current tobe flowed is confined in the current paths 257B. Since the current paths257B function as a conductor for flowing the current perpendicular tothe film surface of the insulating layer 257A, the current paths 257Bmay be made of metallic layers made of Cu or the like. Namely, thespacer layer 257 includes the current confined path structure (CCPstructure) so as to cause and enhance the spin torque effect originatedfrom the current confining effect. The current paths 257B may be made ofAu, Ag, Al, Ni, Co, Fe or an alloy thereof instead of Cu. The diameterof each current path 257B may be set to an order of several nm,concretely, within a range of 1 to 10 nm.

The top metallic layer 257D composes the spacer layer 257 in the broadsense as described above. Then, the top metallic layer 257D functions asprotecting the free layer 258 against the oxide of the spacer layer 257(i.e., a barrier layer against the oxide of the spacer layer 257) anddeveloping the crystallinity of the free layer 258 because the freelayer 258 is formed on the top metallic layer 257D. For example, whenthe insulating layer 257A is made of amorphous layer (e.g., Al₂O₃), thecrystallinity of the metallic layer, that is, the free layer 258 to beformed on the insulating layer 257A is deteriorated. In this case, ifthe top metallic layer 257D is made of a fcc crystallinity-enhancinglayer (e.g., Cu layer), the crystallinity of the free layer 258 can beenhanced remarkably. In this case, the thickness of the top metalliclayer 257D may be set to 1 nm or less.

The top metallic layer 257D may be omitted. The bottom metallic layer257C is a source for forming the current paths 257B and thus, made ofthe same material as the current paths 257B.

In the high frequency oscillator shown in FIG. 14, the current densityin the current paths 257B becomes more than 10⁸ A/cm² originated fromthe current confining effect as described in Reference 2 so that thespin transfer effect is likely to be caused. Namely, the current paths257B functions as a trigger to cause the spin transfer effect.

-   [Reference 2] JP-A 2007-124340 (KOKAI)    According to the spin transfer effect, the high frequency    oscillation can be conducted easily. In other words, it is desired    that the high frequency oscillator contains the current paths 257B,    that is, the nano-current path structure in view of the use of the    high frequency assist in addition to the multi-layer recording and    multi-data recording.

FIG. 15 is a structural view schematically showing the structure ofstill another high-frequency oscillator to be employed in the magneticrecording device in this embodiment. The high frequency oscillator shownin FIG. 15 is modified from the high frequency oscillator shown in FIG.14. In FIG. 14, one spacer layer with nano-current path structure isprovided, but in FIG. 15, two spacer layers with respective nano-currentpath structure are provided. Concretely, the third pinned layer 262 isnewly provided and the pair of spacer layers 257 (two spacer layers 257)are provided so as to sandwich the third pinned layer 262. In the highfrequency oscillator 25 shown in FIG. 15, since two spacer layers 257are provided, the current confining effect can be enhanced so that thespin transfer effect is likely to be caused. Therefore, the highfrequency oscillation can be easily provided.

The concrete structure of the spacer layer 257 in the high frequencyoscillator 25 in FIG. 15 can be formed in the same manner as thestructure of the spacer layer 257 in the high frequency oscillator 25 inFIG. 14. Moreover, other components except the spacer layers 257 in thehigh frequency oscillator in FIG. 15 can be formed in the same manner asthe components in the high frequency oscillator in FIG. 13.

The number of spacer layer is not limited to one or two as described inthe embodiments. For example, the number of spacer layer may be set tothree or more.

FIG. 16 is a structural view schematically showing the structure of afurther high-frequency oscillator to be employed in the magneticrecording device in this embodiment. In the high frequency oscillator 25in FIG. 16, a pair of hard biasing layers 264 are formed on the sides ofthe stacking structure of the underlayer 252 through the cap layer 259between the bottom electrode 251 and the top electrode 260 viarespective insulating layers 263, in comparison with the high frequencyoscillator 25 in FIG. 13. Other components of the high frequencyoscillator 25 in FIG. 16 are configured similar to the components of thehigh frequency oscillator 25 in FIG. 13.

With a high frequency oscillator, the magnetic anisotropy of the freelayer is required to be enhanced so as to realize the high frequencyoscillation. Namely, the free layer must be magnetically hard. In thispoint of view, it is required to apply a biasing magnetic field to thefree layer. In FIG. 16, since the hard biasing layers 264 are formed onthe sides of the stacking structure of the underlayer 252 through thecap layer 259 via the insulating layers 263, respectively, the freelayer 258 is magnetically hard so that the magnetization of the freelayer 258 is unlikely to be rotated.

With a magneto-resistance effect element, the hard biasing layers areprovided so that the magnetic domain of the free layer is renderedsingle. In this point of view, the intensity of the biasing magneticfield from the hard biasing layers is set lower. With the high frequencyoscillator, in contrast, the intensity of the biasing magnetic fieldfrom the hard biasing layers is set higher so that the free layer ismagnetically hard. The use and intention of the hard biasing layers aresimilar to the ones in Reference 2.

The hard biasing layers 263 may be made of CoPt, CoCrPt, CoCr or FePt.

FIG. 17 is a structural view schematically showing the structure of astill further high-frequency oscillator to be employed in the magneticrecording device in this embodiment. In the high frequency oscillator 25in FIG. 17, a pair of current wirings 265 are provided in the sides ofthe stacking structure of the high frequency oscillator 25. Othercomponents in the high frequency oscillator 25 in FIG. 17 are similar tothe ones in the high frequency oscillator 25 in FIG. 13.

In the high frequency oscillator 25 in FIG. 17, the intensity of themagnetic field to be applied to the free layer 258 using the currentmagnetic field from the current wirings 265. The use and intention ofthe current wirings 265 are similar to the ones in Reference 2.Therefore, the frequency of the high frequency oscillation can be easilyincreased to an order of several ten GHz by controlling the magneticfield through the appropriate control of the current magnetic field.

FIG. 18 is a structural view schematically showing the structure ofanother high-frequency oscillator to be employed in the magneticrecording device in this embodiment. The high frequency oscillator shownin FIG. 18 is modified from the high frequency oscillator shown in FIG.17. In FIG. 18, a current wiring 266 is provided above the stackingstructure (top electrode 260) of the high frequency oscillator 25 whilein FIG. 17, the pair of current wirings 265 are provided in the sides ofthe stacking structure of the high frequency oscillator 25. In thiscase, too, the frequency of the high frequency oscillation can be easilyincreased to an order of several ten GHz by controlling the magneticfield through the appropriate control of the current magnetic field.

Particularly not shown, the current wiring 266 may be provided below thestacking structure (bottom electrode 251) of the high frequencyoscillator 25 and another pair of current wirings may be provided aboveand below the stacking structure of the high frequency oscillator 25,respectively.

<Magneto-Resistance Effect Element>

Then, the magneto-resistance effect element to be employed in themagnetic recording device in this embodiment will be described. Asdescribed above, the magneto-resistance effect element may be configuredso as to utilize the principle of the CIP-GMR film, the TMR film or theCPP-GMR film.

The magneto-resistance effect element utilizing the CPP-GMR film may beconfigured as shown in FIGS. 13 to 15 relating to the high frequencyoscillator. The characteristics requiring for the components in themagneto-resistance effect element are set similar to the ones in thehigh frequency oscillator. Herein, the three-layered structure of thesecond pinned layer 256, the spacer layer 257 and the free layer 258functions as a so-called magneto-resistance effect film so as to exhibitthe magneto-resistance effect instead of the high frequency oscillation.According to the magneto-resistance effect, the magneto-resistanceeffect element can detect the magnetic field from a magnetic recordingmedium, and the intensity of the magnetic field therefrom so as to readout the information recorded in the magnetic recording medium.

In the magneto-resistance effect element, a pair of hard biasing layersmay be provided on the sides of the inherent stacking structure of themagneto-resistance effect element. In this case, since the hard biasinglayers are mainly provided so that the magnetic domain of the free layeris rendered single, the biasing magnetic field is set lower differentfrom the hard biasing layers to be employed in the high frequencyoscillator. As described above, in the high frequency oscillator, thebiasing magnetic field is set higher.

Since the magneto-resistance effect element utilizing the CIP-GMRelement or the TMR film is commercially available, an appropriatemagneto-resistance effect element may be selected from among the onescommercially available. For example, the magneto-resistance effectelement utilizing the TMR film can be provided by making the spacerlayer 257 of an insulating film in the high frequency oscillator shownin FIG. 13.

<Hard Disk and Head Gimbal Assembly>

The magnetic head shown in FIGS. 9 to 12 may be incorporated in anall-in-one recording/reproducing magnetic head assembly (HGA) and then,mounted at a magnetic recording/reproducing device. FIG. 19 is astructural view showing the schematic structure of the magneticrecording/reproducing device. FIG. 20 is a structural view showing themagnetic head assembly incorporated in the magneticrecording/reproducing device shown in FIG. 19.

The magnetic recording/reproducing device 300 shown in FIG. 19constitutes a rotary actuator type magnetic recording/reproducingdevice. In FIG. 19, a magnetic recording disk 370 is mounted to aspindle 310 to be turned in the direction designated by the arrow A by amotor (not shown) which is driven in response to control signals from adrive unit controller (not shown). In FIG. 19, the magneticrecording/reproducing apparatus 300 may be provided with a singlemagnetic recording disk 370, but with a plurality of magnetic recordingdisks 370.

A head slider 320, which functions as recording/reproducing informationto be stored in the magnetic recording disk 370 is mounted on a tip of asuspension 330 of a thin film type. The head slider 320 mounts at thetip the magnetic head containing the magnetic resistance effect elementas described in above embodiments.

When the magnetic recording disk 370 is rotated, such a surface (ABS) ofthe head slider 320 as being opposite to the magnetic recording disk 370is floated from on the main surface of the magnetic recording disk 370.Alternatively, the slider may constitute a so-called “contact runningtype” slider such that the slider is in contact with the magneticrecording disk 370.

The suspension 330 is connected to one edge of the actuator arm 340 witha bobbin portion supporting a driving coil (not shown) and the like. Avoice coil motor 350 being a kind of a linear motor is provided at theother edge of the actuator arm 340. The voice coil motor 350 is composedof the driving coil (not shown) wound around the bobbin portion of theactuator arm 340 and a magnetic circuit with a permanent magnet and acounter yoke which are disposed opposite to one another so as tosandwich the driving coil.

The actuator arm 340 is supported by ball bearings (not shown) providedat the upper portion and the lower portion of the spindle 360 so as tobe rotated and slid freely by the voice coil motor 350.

As shown in FIG. 20, the magnetic head assembly 400 has the actuator arm340 with the bobbin portion supporting the driving coil and the like.The suspension 330 is connected with the one edge of the actuator arm340. Then, the head slider 320 with the magnetic head containing themagneto-resistance effect element as defined in above-embodiments isattached to the tip of the suspension 330. The suspension 330 includes alead wire 410 for writing/reading signals, where the lead wire 410 iselectrically connected with the respective electrodes of the magnetichead embedded in the head slider 320. In the drawing, reference numeral“420” denotes an electrode pad of the assembly 400.

In the magnetic recording/reproducing device and the magnetic headassembly shown in FIGS. 19 and 20, since the magnetic head containingthe high frequency oscillator as shown above is provided, the intendedmulti-layer recording and multi-data recording can be realized and thereproducing of the data recorded in the magnetic recording mediumthrough the multi-layer recording and multi-data recording can be alsorealized.

Although the present invention was described in detail with reference tothe above examples, this invention is not limited to the abovedisclosure and every kind of variation and modification may be madewithout departing from the scope of the present invention.

What is claimed is:
 1. A magnetic recording device, comprising: arecording medium comprising: a plurality of recording layers, eachrecording layer having a different thickness, a different ferromagneticresonance frequency f′, and a different coercivity in the absence ofhigh frequency oscillation, wherein the ferromagnetic resonancefrequencies of the recording layers differ from one another by at least1 GHz; a magnetic recording head for writing information to the magneticrecording medium, the magnetic recording head including a high frequencyoscillator selectively changeable between a first oscillation frequencyf1 and a second oscillation frequency f2, wherein said first oscillationfrequency f1 causes ferromagnetic resonance in a first set of recordinglayers and does not cause ferromagnetic resonance in each recordinglayer not included within said first set of recording layers, whereinsaid second oscillation frequency f2 causes ferromagnetic resonance in asecond set of recording layers and does not cause ferromagneticresonance in each recording layer not included within said second set ofrecording layers, said second set of recording layers differing fromsaid first set of recording layers, wherein when said first oscillationfrequency is selected, magnetization directions of all recording layersin the first set of recording layers are written by a magnetic fieldfrom the magnetic recording head, said magnetic field being less than amagnetic field which would be required to write to any recording layernot included within said first set of recording layers, wherein whensaid second oscillation frequency is selected, magnetization directionsof all recording layers in the second set of recording layers arewritten by a magnetic field from the magnetic recording head, saidmagnetic field being less than a magnetic field which would be requiredto write to any recording layer not included within said second set ofrecording layers; and a magnetic reproducing head for reading outinformation from the magnetic recording medium, wherein said highfrequency oscillator functions as a magneto-resistance effect element insaid magnetic reproducing head.
 2. The device as set forth in claim 1,wherein the magnetic reproducing head detects an intensity of a magneticfield caused from a total amount of magnetization of the plurality ofrecording layers, and reads out information recorded in the magneticrecording medium based on the detected intensity.
 3. The device as setforth in claim 1, wherein the ferromagnetic resonance frequencies of therecording layers differ from one another by at least 1 GHz.
 4. Thedevice as set forth in claim 1, wherein each recording layer includes atleast one element selected from the group consisting of Co, Fe, Ni andPt and contents of the at least one element in the respective pluralityof recording layers differ from one another by five atomic percent ormore.
 5. The device as set forth in claim 1, wherein the plurality ofrecording layers are magnetically separated with respective magneticseparating layers including a non-magnetic element.
 6. The device as setforth in claim 5, wherein each of the magnetic separating layersincludes at least one element selected from the group consisting of Ru,Pd, Ir and Pt.
 7. The device as set forth in claim 1, whereinnon-magnetic material is provided between tracks in the magneticrecording medium.
 8. The device as set forth in claim 1, wherein theoscillating frequency of the high frequency oscillator is set within afrequency range of a ferromagnetic resonance frequency of the at leastone recording layer ±1 GHz or less.
 9. The device as set forth in claim1, wherein a relation of f1=n×f′/2 (n: integer) is satisfied when anoscillating frequency of the high frequency oscillator is designated byf1 and a magnetic resonance frequency of the first set of recordinglayers is designated by f′, and wherein a relation of f2=n×f′/2 (n:integer) is satisfied when an oscillating frequency of the highfrequency oscillator is designated by f2 and a magnetic resonancefrequency of the second set of recording layers is designated by f′. 10.The device as set forth in claim 1, wherein an oscillating frequency ofthe high frequency oscillator changes on the order of 1 GHz or more. 11.The device as set forth in claim 10, wherein the high frequencyoscillator is interposed between two hard magnetic layers.
 12. Thedevice as set forth in claim 10, wherein the high frequency oscillatorincludes a free layer and a current wiring, the current wiring applyinga current magnetic field to the free layer.
 13. The device as set forthin claim 1, wherein the high frequency oscillator includes a stackedstructure comprising at least a fixed magnetization layer, a spacerlayer and a free layer, and a pair of electrodes for current flowperpendicular to a film surface of the stacked structure formed at endsurfaces of the stacked structure.
 14. The device as set forth in claim13, wherein the spacer layer includes an insulating layer and metalliclayers formed through the insulating layer so as to function as pathsfor flowing a current between the fixed magnetization layer and the freelayer.
 15. The device as set forth in claim 14, wherein the insulatinglayer includes at least one element selected from the group consistingof Al, Ti, Hf, Mg, Zr, Mo, Si, Cr, Nb, Ta, W, B, C and V, and whereineach of the metallic layers contains at least one element selected fromthe group consisting of Cu, Au, Ag, Al, Fe, Co and Ni.
 16. The device asset forth in claim 14, wherein a diameter of each of the metallic layersis in a range of 1 to 10 nm.
 17. The device as set forth in claim 1,wherein the high frequency oscillator is configured such that a currentto flow in use as the magneto-resistance effect element is set lowerthan a current to flow in use as an inherent oscillator.
 18. A magneticrecording device for use with a magnetic recording medium including aplurality of recording layers, each recording layer having a differentthickness, a different ferromagnetic resonance frequency f, and adifferent coercivity in the absence of high frequency oscillation,wherein the ferromagnetic resonance frequencies of the recording layersdiffer from one another by at least 1 GHz, the magnetic recording devicecomprising: a magnetic recording head for writing information to themagnetic recording medium, the magnetic recording head including a highfrequency oscillator selectively changeable between a first oscillationfrequency f1 and a second oscillation frequency f2, wherein said firstoscillation frequency f1 causes ferromagnetic resonance in a first setof recording layers and does not cause ferromagnetic resonance in eachrecording layer not included within said first set of recording layers,wherein said second oscillation frequency f2 causes ferromagneticresonance in a second set of recording layers and does not causeferromagnetic resonance in each recording layer not included within saidsecond set of recording layers, said second set of recording layersdiffering from said first set of recording layers, wherein when saidfirst oscillation frequency is selected, magnetization directions of allrecording layers in the first set of recording layers are written by amagnetic field from the magnetic recording head, said magnetic fieldbeing less than a magnetic field which would be required to write to anyrecording layer not included within said first set of recording layers,wherein when said second oscillation frequency is selected,magnetization directions of all recording layers in the second set ofrecording layers are written by a magnetic field from the magneticrecording head, said magnetic field being less than a magnetic fieldwhich would be required to write to any recording layer not includedwithin said second set of recording layers; and a magnetic reproducinghead for reading information from the magnetic recording medium, whereinsaid high frequency oscillator functions as a magneto-resistance effectelement in said magnetic reproducing head.
 19. A magnetic recordingdevice for use with a magnetic recording medium including a plurality ofmagnetically separated recording layers, each recording layer having adifferent thickness, a different ferromagnetic resonance frequency f′,and a different coercivity in the absence of high frequency oscillation,wherein the ferromagnetic resonance frequencies of the recording layersdiffer from one another by at least 1 GHz, the magnetic recording devicecomprising: a magnetic recording head for recording information to themagnetic recording medium, the magnetic recording head including a highfrequency oscillator selectively changeable between a first oscillationfrequency f1 and a second oscillation frequency f2, wherein said firstoscillation frequency f1 causes ferromagnetic resonance in a first setof recording layers and does not cause ferromagnetic resonance in eachrecording layer not included within said first set of recording layers,wherein said second oscillation frequency f2 causes ferromagneticresonance in a second set of recording layers and does not causeferromagnetic resonance in each recording layer not included within saidsecond set of recording layers, said second set of recording layersdiffering from said first set of recording layers, wherein when saidfirst oscillation frequency is selected, magnetization directions of allrecording layers in the first set of recording layers are written by amagnetic field from the magnetic recording head, said magnetic fieldbeing less than a magnetic field which would be required to write to anyrecording layer not included within said first set of recording layers,wherein when said second oscillation frequency is selected,magnetization directions of all recording layers in the second set ofrecording layers are written by a magnetic field from the magneticrecording head, said magnetic field being less than a magnetic fieldwhich would be required to write to any recording layer not includedwithin said second set of recording layers; and a magnetic read head forreading out information from the magnetic recording medium, wherein saidhigh frequency oscillator functions as a magneto-resistance effectelement in said magnetic read head.